1. Field of the Invention
The present invention relates to semiconductor memory devices.
2. Description of the Related Art
A dynamic random access memory (DRAM) is a semiconductor memory device where one bit of data can be stored with use of one transistor and one capacitor. The DRAM has a small area per memory cell, easiness in integration for modularization, and is manufactured at low cost.
In a DRAM, electric charges stored in a capacitor are leaked due to off-state current of a transistor, and thus an operation of recharge (refresh) is required before charges are lost.